Wait for your device to restart, at which time you'll see a You are in recovery mode screen. Press Ctrl + D to dismiss the message. Now you're all set with Developer Mode on your Chromebook.
Developer Mode on Chromebooks allows you to install ChromeOS Canary and Android APKs. The Linux apps environment in ChromeOS doesn't require Developer Mode. You can enable Developer Mode with a button combination or keyboard shortcut.
Learn how to turn on ChromeOS Developer Mode in a step-by-step tutorial. We have also mentioned how you can go back to the normal mode.